Field of the Invention
The present invention mainly relates to centrifugal clutches for small engines that drive work machines such as bush cutters.
Description of Related Art
For a small engine having a centrifugal clutch, for example, during acceleration of the engine, engagement of the clutch is started at or around a time when the rotation rate of the engine or the engine speed reaches 3800 rpm, and the clutch is completely engaged when the engine speed reaches about 7000 rpm. An unusual sound may be generated in a partially-engaged clutch state where the clutch is shifting from the start of engagement of the clutch to the complete engagement of the clutch. Such an unusual sound is generated, for example, as follows.
When the engine speed is increased to start engagement of the clutch, the engine speed is reduced due to a load of a cutting blade, and thus, the clutch may be disengaged. Also in this state, the cutting blade continues to rotate due to inertial force. When the clutch is disengaged, the rotation of the cutting blade is gradually reduced, and then, the engine speed is increased again due to reduction of the load, to restart engagement of the clutch. The engine speed is then reduced due to the load of the cutting blade, to disengage the clutch again. Thus, since engagement and disengagement of the clutch are repeated, contact between a clutch shoe and a clutch drum is repeated to generate an unusual sound.
In order to reduce generation of such an unusual sound, it has been known that a holder plate is mounted to one of side surfaces of the clutch shoe, and a pressing plate is mounted to the other of the side surfaces of the clutch shoe, to hold the clutch shoe between the holder plate and the pressing plate (Japanese Laid-Open Utility Model Publication No. H04-106532). In Japanese Laid-Open Utility Model Publication No. H04-106532, the clutch shoe is elastically held from both the side surfaces by the holder plate and the pressing plate, thereby reducing unstable operation of the clutch shoe to reduce generation of an unusual sound.
However, according to Japanese Laid-Open Utility Model Publication No. H04-106532, two components (the holder plate and the pressing plate) are necessary, and each plate has four pressing portions, thereby complicating the structure. Furthermore, the clutch shoe needs to have receiver portions for receiving the pressing portions, thereby limiting the structure of the clutch shoe.